Aqueous slurry plasticization of polyvinyl acetal resins



AQUEWUS SLURRY PLASTlClZATlON F POLY- VINYL ACETAL RESILJS BarnardMitchel Marks, Wilmington, Del, assignor to E. l. tlu Pont de Nernoursand Company, Wilmington, DeL, a corporation of Delaware No Drawing.Application August 15, 1956 Serial No. 604,069

3 Claims. (Cl. 260-2.6)

This invention relates to a process for plasticizing polyvinyl acetalresins, and, more particularly, it relates to a process in whichpolyvinyl butyral particles are slurried with water and a liquidplasticizer, and the resultant slurry is agitated until the plasticizeris absorbed by the particles.

This is a continuation-in-part of copending application Serial Number449,018, filed August 10, 1954, now abandoned.

' It is known that polyvinyl acetal resins find a wide use in thepreparation of safety-glass laminations in which the polyvinyl acetalresin is an interlayer between two sheets of glass. In order for theresin to be useful in such an interlayer, it must be plasticized so thatthe resin is soft and tacky and will adhere tenaciously to glass. Theprior art methods of plasticizing polyvinyl acetal resins have takenfour general directions; the first eing a plasticization of the resin insolution, the second being a plasticization of the resin in the form ofa melted mass, the third being the plasticization of dry granular resin,and the fourth being the plasticization of resin in a colloidalsuspension. The first method requires subsequent process steps to removethe resin solvent after the extrusion of the plasticizedresin into theform of a sheet or other article for ultimate use elsewhere. The secondmethod requires the use of powerful conveying equipment such as screwdevices and the like to transport the heavy viscous melted polyvinylacetal resin. The third method requires the employment of large andexpensive drying equipment to dry the polyvinyl acetal resin prior toplasticization. of a dispersing agent and heat or work to incorporatethe plasticizer into the resin, following which, the dispersing agentmust be removed if the resin is to be used as an interlayer in glasslaminates.

It is an object of this invention to provide a novel and simple processfor plasticizing polyvinyl acetal resin. It is another object of thisinvention to provide a method for plasticizing polyvinyl acetal resin inthe form of an aqueous slurry of resin particles which are notselfdispersible. Another object of this invention is to provide aprocess for effecting a uniform and accurately predictable distributionof plasticizer throughout a particulate mass of polyvinyl acetal resin.It is still another object of this invention to provide a speedy andsimplified process for plasticizing polyvinyl acetal resins in a formsuch that the plasticized resin may be transported through pipelines byordinary pumping equipment to the next processing step without thenecessity of removing a solvent, removing a wetting agent or adispersing agent, or in changing the resin slurry in any form. Stillanother object is to provide a composition of water and plasticizedpolyvinyl acetal resin which may be employed as a feed to an extrusiondevice. Other objects will appear in the more detailed explanation ofthis invention which follows.

The above objects are accomplished in accordance with The fourth methodrequires'the use 2,864,784 Patented Dec. 16,1958.

aqueous slurry of polyvinyl acetal resin particles, which readilyseparate from the aqueous medium in the absence of agitation, adding thedesired amount of waterinsoluble ester plasticizer such that theproportion of (water) to (resin plus plasticizer) is from about 3:1 toabout 20:1 by weight, and continuing the agitation, in the absence of adispersing agent, for a period of time suflicient to allow theplasticizer to be absorbed by the resin particles. This slurry may thenbe transported by pumps and pipelines to a succeeding process step, e.g., an extruder for dewatering, mixing, melting, and extruding the resininto the form desired.

In the preferred embodiment of this invention, a slurry is formedcontaining from about 4 to 10 parts by weight of water to 1 part ofresin. While this slurry is being agitated, plasticizer in the amount ofabout 10% to about 50% by weight of the unplasticized resin is added andthe agitation is continued. The preferred plasticizers are from thegroup consisting of triethylene glycol di- (2-ethyl butyrate),di(beta-butoxyethyl)adipate, and dibutyl sebacate. The agitated slurryis maintained at a temperature from about 20 to about 65 C. over aperiod of 10 to minutes until substantially all of the plasticizer isabsorbed by the resin, thereby producing a uniform aqueous slurry ofplasticized polyvinyl acetal resin. The preferred polyvinyl acetal resinfor use in the preparation of safety glass is a partial polyvinylbutyral resin which is defined as meaning a polymer having from about18% to about 25% by weight of vinyl alcohol groups, not more than about2% by weight of vinyl acetate groups, and the remainder being vinylbutyral groups.

The term slurry wherever used in this description and in the appendedclaims is intended to mean a mixture of a liquid and an insoluble solidwhich is in the form of particles which are of such a size, structure,and density that the particles do not remain suspended in the liquidwhen the mixture is not agitated. Polyvinyl butyral has a specificgravity of about 1.15, depending on its composition, and polyvinylformal has a specific gravity of about 1.2-1.3. A typical screenanalysis (U. S. Sieve Series) on polyvinyl butyral employed in thisprocess is shown below:

The largest fraction of this material is, therefore, from about 0.02 to0.04 inch in particle diameter, which, combined with its density, is amaterial which might be expected to settle rapidly in quiescent water.All particles of polyvinyl butyral, however, are not alike, probablybecause the particles, in some instances, are agglomerates of smallerunits. Some of these agglomerated particles entrap' air in theirinterstices, and tend to float, while other particles settle ratherrapidly in water. In any event, the particles of polyvinyl butyral donot form a suspension after the nature of colloidal suspensions or thosesuspensions formed with the aid of a wetting agent or a dispersingagent.

The process of this invention is particularly designed to producepolyvinyl butyral for eventual use as an interlayer in automotive safetyglass. For such a use the polyvinyl butyral must have an unimpairedadhesiveness in order that it may bond tightly to the glass with whichit is laminated. It has been found that, if a dispersing agent isemployed in the process of this invention, the adhesive- 3 ness of theresulting product is reduced to the extent that it cannot be employedfor use in laminating glass. On the other hand, it is necessary to thepresent process that the resin particles be dispersed throughout theaqueous phase in some fashion so that the plasticizer may contact eachresin particle, and that each particle absorb plasticizer into itsinterior rather than merely on the surface. If a surface adsorption onlyis achieved the resin bleeds, which term is employed in the'trade tomean glycol dit 2-ethy1 butyrate) as a plasticizer, and the agitationand temperature kept constant during the reaction time. The productslurry was then removed from the kettle and the water was analyzed forplasticizer to determine, by ditference, the amount of plasticizerabsorbed by the resin particles. The details of these examples arelisted in the following table. Example 6 illustrates the formation ofagglomerates of the plasticized resin due to a low water:resin ratio anda slow agitator speed.

Table Charge Process conditions 7 Wet poly- (Water): Percent ExampleDistilled Plastivinyl Tern- Agitator (resin Plastici- Kettle plnsti-Remarks water, cizer, butyral peruspeed, plus zation size, cizer poundspounds resin ture, R. P. M. plastitime, gallons absorbed (40% C. cizer),minutes by resin water ratio Pounds 1 l. 230 6.45 25.0 =-50 1, 725 11:125 50 99.3 Good dispersion. 2 230 9.10 35. 45 1, 725 8:1 15 50 08. 7 Do.3 250 4. 3 17. 25 41 1, 725 17. :1 10 5 9'. 9 D0. 1 625 23. 8 90. O 3696 8:1 100 09. .3 Do. 5 625 26. 8 100. 0 90 7. 5:1 100 90. 1 Do. 6 50032.6 125.0 38 96 5:1 15 100 99. 5 Eilfltlll agglomerntes ormcd. 7 1608.1 31. 25 33 1,725 6:1 30 08.2 Good dispersion.

that the plasticizer exudes from the resin as small drop- 90 Example 8.Aslurry is prepared containing 40 gallons lets, leaving the resin in anunplasticized condition. The process of this invention employs anagitated mixture of water, resin and plasticizer, in the absence of adispersing agent, to produce a completely plasticized resin productwhich does not bleed. The agitation is employed to provide an intimatemixture of the plasticizer and resin particles, and, at the same time,to prevent the tacky resin particles from agglomerating during the timein which the resin is absorbing the plasticizer.

In United States Patent 2,720,501, issued to R. T. Van Ness on October11, 1955, there is described a process for the preparation of polyvinylacetal resins in which polyvinyl alcohol is prepared as described aboveand is then condensed with aldehyde in the presence of water. Thecondensation product of this process is a heterogeneous mixture, orslurry, of polyvinyl acetal resin particles in water, rather than athick viscous solution as prepared in the heretofore known processes. Atypical screen analysis of such resin particles shows that at least 90%by weight of the particles is retained on a -meth screen (U. S. SieveSeries), and about %-80% is retained on a 35-mesh screen. It istherefore apparent that the condensation product is already in the formof an aqueous slurry as required for the present process of plasticizingand that such an aqueous condensation product does not have to besubjected to a series of process steps before it may be utilized in theprocess of the present invention. Polyvinyl butyral, prepared by otherknown processes, may also be employed in the present invention, althoughthe particles must be free of any wetting agent or dispersing agent, andof suflicient size not to be self-dispersible.

In examples which are given below to illustrate various embodiments ofthis invention, parts and percentages are by weight unless otherwisespecified.

Examples 1 to 7.-In' each of these examples the dry unplasticizedpolyvinyl butyral flake was added to distilled water in a steam jacketedresin kettle fitted with a propeller-type agitator. The particle size ofthe flake was such that about 15% would be retained on a 35-mesh screen,about 73% would be retained on an -mesh screen, and the remainder wouldpass through an 80- mesh screen (U. S. Sieve Series). The mixture ofresin and water was agitated and heated to form a slurry at theindicated temperatures. There was then added triethylene of water and 28pounds of polyxinyl butyral resin. While this slurry is being agitatedthere is added 11.3 pounds of di(beta-butoxy ethyl)adipate. The pH ofthe slurry is 7.2. The slurry is agitated at 40 C. for about 20 minutes.The slurry was then fed into a screw extrudcr after passing through adevice for removing a large portion of the water and extruded in theform of a sheet. At the end-of this time, measurements are made onsamples of the resin sheet to determine the amount of absorbedplasticizer present in the resin. The amount of dibutyl Cellosolveadipate present is about 29% by weight of the plasticized resin. Thedetermination is made by measuring the index of refraction of theplasticized resin and transforming this measurement to plasticizercontent, by means of previously obtained correlations between indexofrefraction values and concentrations determined by distillation andseparation of the resin constituents.

Example 9.-The procedure of Example 8 is repeated except that theplasticizer used is dibutyl sebacate in the amount of 10.5 pounds, andthe slurry is agitated at 50 C. rather than 40 C. as was the case inExample 8. The plasticized resin was then formed into a sheet byextrusion from ascrew extruder. The amount of absorbed dibutyl sebacateplasticizer is found to be 26.0% by weight of the plasticized resin. Ina second identical experiment the amount of absorbed dibutyl sebacatewas found to be 25.2% by weight of the plasticized resin.

Example 10.-Tests are made to determine the extrusion pressure andtemperature when plasticized polyvinyl b'utyral resin particles, similarto those prepared in Examples 1-9, are employed and fed to a screwextrusion device. It is found that when the feed material is dry, theextrusion pressure is 1500 to 1600 pounds per square inch and thetemperature of the material rises to about 185 C. by reason of thefriction forces on the resin mixture in the extrusion device. In thesame device if the feed material is a mixture of approximately 30% waterand 70% plasticized resin, the extrusion pressure is only 1100 poundsper square inch and the temperature of the resin rises to only about C.

In the examples given above, there are illustrations of a process forplasticizing partial polyvinyl butyral resin with triethylene glycoldi(2-ethyl butyrate), di(betabutoxy ethyl)adipate, and dibutyl sebacateas plasticizers. It is to be understood that this invention is notintended to be limited to the use of these particular plasticizers sincethis process is equally applicable ;to-the-plasticization of otherpolyvinyl acetal resins and :to the .use of other known water-insolubleester plasticizers.

The amount of plasticizer which may beu'sed will vary with the resin tobe plasticized, the plasticizer employed, and the degree ofplasticization required. In general, the use of plasticizer in an amountless than about by weight of the unplasticized resin will be insuficientto achieve any noticeable plasticization, and amounts of more than about50% to 60% imparts undesirable characteristics to the resin. Thepreferred amount of plasticizer is from about to about 50% by weight ofthe unplasticized resin. In the plasticization of polyvinyl butyral withtriethylene glycol di(2-ethyl butyrate), di(beta-butoxy ethyl).adipate,or dibutyl sebacate, the amount of plasticizer recommended. is fromabout to about 45% by 'weightof the'unplasticized polyvinyl butyral.

The resins which may be plasticized by'the process of thisinventioninclude the polyvinyl acetal-resins resulting from thecondensation of polyvinyl alcohol'with a-lower aliphatic aldehyde,preferably those containing 2 w 6 carbon atoms, such as'acetaldehyde,propionaldehyde, butyraldehyde, valeraldehyde, and 'hexaldehyde. Sincethe polyvinyl alcohol starting'material normallycontains'someunhydrolyzed acetyl groups, and sincethe nature of the acetal reactionis such that some alcoholic hydroxyl' groups fail to react with thealdehyde, the resulting resin is a heterogeneous structure of vinylacetate units, vinyl alcohol units, and vinyl acetal units. Suchaheterogeneous resin is known to those skilled in the .art, and isherein called, a partial polyvinyl acetal resin. The partial polyvinylacetal resin employed in this invention is that product resulting'fromthe partial acetalization of a polyvinyl alcohol containing notmore-than about 2% by weight of unhydrolyzed vinyl acetate groups. Thedegree of acetalization may vary with the product desired and thealdehyde used. In general, the degree of acetalization may be from about30% to about 95% complete, the lower degree of acetalization beingemployed with the higher aldehydes and the higher degree ofacetalization being employed with the lower aldehydes. In the preferredembodiment of this invention wherein polyvinyl butyral is prepared foruse as a safety-glass interlayer the degree of acetalization withbutyraldehyde will be from about 64% to about 75% complete. The finalpolyvinyl butyral product will therefore contain not more 18%25% vinylalcohol groups, and the remainder vinyl butyral groups.

The slurry which is used in the process of this invention consistsessentially of water, resin, and plasticizer. No dispersing agent ispresent in the slurry. The amount of Water is that which is necessaryfor the maintenance of a fluid, low-viscosity slurry. It has been foundthat if the (water):(resin plus plasticizer) ratio is less than about3:1, it is extremely difiicult to prevent agglomeration of the resinparticles without the consumption of abnormally large amounts of powerin agitation of the slurry. The upper limits of the (water) :(resin plusplas- ,ticizer) ratio are dictated primarily by considerations ofeconomy and practicality since the use of high ratios of (water):(resinplus plasticizer) would entail larger and larger equipment, higherheatingloads, and so forth, Without any compensating advantages. Thepreferred upper limit of (water):(resin plus plasticizer) ratio is about20:1 since beyond this point no further advantages have been experiencedin preventing agglomeration of the particles and in effecting economy byreducing the power requirements of agitation as against the increasedcost of larger equipment. The preferred range of (water) (resin plusplasticizer) is from about 4:1 to about 10:1. In some embodiments ofthis invention a portion of the unplasticized resin may be replaced byshredded scrap resin which has been previously plasticized. The propor-.uneconomical.

tion of unplasticizedresin to plasticized scrap :will vary according totheamount of scrap on hand, but normally it is .not less than about 2:1.

The temperature of the plasticizing process is governed by many factors.If the temperature is too'low, the'plasticization time becomesinordinately long and therefore If the plasticization temperature is toohigh, the resin particles tend to soften and to agglomerate into a solidor semi-solid mass, and, therefore, more agitation or higher (water):(re'sin plus plasticizer) ratios are required to maintain the desiredmixture of resin and plasticizer. The temperature limits for :theprocess of this invention are from about 20 C. to about 65 C. Thepreferred temperatures are fromv about 35 C. to about 55 C. forthe'plasticization of polyvinyl butyral.

The time required to accomplish plasticization may vary from about10-100 minutes depending upon-conditions of temperature agitation, andconcentration, although preferred conditions will permit theplasticization to-take'place in about 10-30 minutes. The elapse of timeis required merely to allow the polyvinyl acetalresin to absorbsubstantially all of the plasticizer, in distinction to the surfaceadsorption of plasticizer which eventually results in bleeding of theplasticizer. In 10 to 30 minutes in most embodiments of this invention,at least of the plasticizer will be absorbed by the resin, and since theslurry of plasticized resin formed in this process is employed as a feedto an extrusion device, there is an assurance that the first :resin fedto the extruder has essentially the same plasticizer concentration asthe last portion of resin entering the extruder. An excess ofplasticizer-would permit some portions of resin to contain moreplasticizer than other portions since at longer contact times a givenamount of resin will absorb a greater amount of plasticizer from theaqueous medium. This process therefore provides a method of obtaining auniform distribution of the plasticizer throughout the resin and anexact concentration of plasticizer in the resin without employing heator powerful mixing devices or solvents for the resin. Stepwiseintroduction of plasticizer may be employed in certain embodiments ofthis invention.

It is important to the process of this invention that the resin bemaintained in an unagglomerated form, without the aid of a dispersingagent, during and after the plasticizing step. As explained above, thiscondition may be aidedby increasing the (water); (resin plusplasticizer) ratio, or by lowering the operating temperature, or both.However, it has been found necessary to employ sufficient agitation ofthe slurry in order to maintain the resin particles in a dispersedcondition and thereby permitting the (water):(resin plus plasticizer)ratio and the operating temperature to be maintained within practicallimits. The amount of agitation normally employed in this process isthat which consumes from about 1 to about 5 horsepower per 1000 gallonsof slurry. Typical peripheral speeds of a paddle agitator are from about600 to 1200 feet per minute in the process of this invention.

An unexpected advantage of the process of this invention is that theslurry of plasticized resin may be employed after removal of sufl'icientwater to form a mixture of about 30% water and 70% plasticized resinsolids in a feed to an extrusion apparatus designed to produce polyvinylacetal sheeting which may be utilized in the preparation of laminatedsafety glass. Since safety-glass interlayer must meet rigid opticalrequirements, it has been necessary that the interlayer be preparedunder carebecame discolored and its optical qualities were therebydestroyed. The slurry of plasticized resin, after being dewateredsomewhat, may be fed into a screw extrusion device which successivelywrings out much of the remaining water from the resin and transforms theremaining mixture of water and plasticized resin into a single-phase,homogeneous low viscosity plastic mass which may be successfullyextruded into sheet form without being heated to the high temperaturesinvolved in previously known extrusion devices, and accordingly producessafety-glass interlayer having acceptable optical qualities.

This process is particularly useful in the manufacture of polyvinylbutyral resin which may be transformed into sheeting for ultimate use asan interlayer in safety glass. Other uses for plasticized polyvinylacetal resins are well known to those skilled in the art.

I claim:

1. A process for plasticizing a partial polyvinyl acetal resincomprising (a) forming an aqueous slurry consisting essentially of (1)particles of an unplasticized partial polyvinyl acetal resin having asize such that at least 90% by weight of said particles will be retainedon a 60-mesh screen (U. S. Sieve Series), said resin being thecondensation product of polyvinyl alcohol and an aldehyde having 2 to 6carbon atoms per molecule, (2) a water-insoluble ester plasticizer forsaid resin which is present in the amount of 10% to 50% by weight ofsaid resin, and (3) water in an amount such that the weight ratio of(water): (resin plus plasticizer) is from 3:1 to 20:1; (b) agitatingsaid aqueous slurry for a period of 10 to 100 minutes at a power inputof at least 1 horsepower per 1000 gallons of slurry; (c) maintaining thetemperature of said slurry from 20 C. to 65 C. during the agitation; and(d) re covering an aqueous slurry of non-bleeding, plasticized partialpolyvinyl acetal resin particles containing at least 90% of theplasticizer originally added to said slurry.

2. The process of claim 1 in which the partial polyvinyl acetal resin ispolyvinyl butyral containing 18%-25% by weight of unacetalized polyvinylalcohol, not more than about 2% by weight of polyvinyl acetate, and theremainder is polyvinyl'butyral; and in which the plasticizer is selectedfrom the group consisting of triethylene glycol di(2-ethyl butyrate),di(beta-butoxy ethyl)adipate, and dibutyl sebacate.

'3. A process for plasticizing polyvinyl butyral resin consistingessentially of (a) forming an aqueous slurry consisting of (1)unplasticized polyvinyl butyral particles which are of such a sizedistribution that at least 90% by weight of said particles are retainedon a -mesh U. S. Sieve Series Screen, said polyvinyl butyral containing18%25% by weight of unacetalized polyvinyl alcohol, 0%2% by weight ofpolyvinyl acetate, and the remainder polyvinyl butyral, (2) 0-50% byweight of said unplasticized resin of previously plasticized polyvinylbutyral, (3) 10%-50% by weight of said unplasticized resin of aplasticizer from the group consisting of triethylene glycol di(2-ethylbutyrate), di(beta-butoxy ethyl)adipate, and dibutyl sebacate, and (4)water in an amount such that the ratio of (water) :(resin plusplasticizer) is from 4:1 to 10:1; (b) agitating said slurry for a periodof 10-100 minutes at an agitation power input of 1-5 horsepower per 1000gallons of slurry and at a temperature of 35 C. to 55 C.; and (c)recovering polyvinyl butyral containing at least of the said plasticizeroriginally added to said slurry.

References Cited in the file of this patent UNITED STATES PATENTS UNITEDSTATES PATENT OFFICE CERTIFICATE 0F QQRRECTION Patent No, 2 864384December 16 1,958

Barnard Mitchel Marks It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correctionand that the said Letters Patent should read as corrected below.

Columns 3 and 4, in the Table tenth column thereof 9 under the heading"Percent plasticizer absorbed by resin", third item. for "9 9" read 9509column 5, line 48, after "not more" insert then about 2% by Weight ofvinyl acetate groups, o

Signed and sealed this 31st day of March 1959,

Attest:

KARL AXLINE ROBERT C. WATSON Commissioner of Patents Attcsting Officcr

1. A PROCESS FOR PLASTICIZING A PARTIAL POLYVINYL ACETAL RESINCOMPRISING (A) FORMING A AQUEOUS SLURRY CONSISTING ESSENTIALLY OF (1)PARTICLES OF AN UNPLASTICIZED PARTIAL POLYVINYL ACETAL RESIN HAVING SIZESUCH THAT AT LEAST 90% BY WEIGHT OF SAID PARTICLES WILL BE RETAINED ON A60-MESH SCREEN (U.S. SIEVE SERIES), SAID RESIN BEING THE CONDENSATIONPRODUCT OF POLYVINYL ALCOHOL AND AN ADEHYDE HAVING 2 TO 6 CARBON ATOMSPER MOLECULE, (2) A WATER-SOULBLE ESTER PLASTICZER FOR SAID RESIN WHICHIS PRESENT IN THE AMOUNT OF 10% TO 50% BY WEIGHT OF SAID RESIN, AND (3)WATER IN AMOUNT SUCH THAT THE WEIGHT RATIO OF (WATER): (RESIN PLUSPLASTICIZER) IS FROM 3:1 TO 20:1 (B) AGIATING SAID AQUEOUS SLURRY FOR APERIOD OF 10 TO 100 MINUTES AT A POWER INPUT OF AT LEAST 1 HORSEPOWERPER 1000 GALLIONS OF SLURRY: (C) MAINTAINING THE TEMPERATURE OF SAIDSLURRY FROM 20*C. TO 65*C DURING THE AGITATION; AND (D) RECONVERTING ANAQUEOUS SURRY OF NON-BLEEING, PLASTICIZED PARTIAL POLYVINYL ACETAL RESINPARTICLES CONTAINING AT LEAST 90% OF THE PLASTICIZER ORDINALLY ADDED TOSAID SLURRY